1. Field of the Invention
This invention relates to heads for blowing sand into moulds for the production of foundry cores.
2. Description of the Prior Art
The mass production of foundry cores involves the use of moulds or core-boxes, usually mounted onto presses, and into which the sand is blown by a jet of air, in order to obtain a compact and even arrangement of sand in the mould.
Known blowing heads comprise stationary components forming a stationary assembly including an upper hopper for storing the sand, a tank placed beneath the hopper suitable for receiving metered quantities of sand, both the hopper and the tank being axial arrangement with respect to the closing plane of the dies forming the mould or core-box, a pressurized air accumulator offset from the axis and connected to the tank by means of valves which periodically let the jet of air pass through the tank to blow the metered quantity of sand in the tank into the mould.
The sand falls from the hopper into the tank through a gated opening which can close-off the hopper from communication with the tank.
Such a system has disadvantages.
A first disadvantage is that the position of the pressurized air accumulator with respect to the tank results in tortuous air pressure lines whose cross-section is restrictive, so that in order to obtain the air pressure required at the tank and to overcome the frictional losses in air pressure, the air pressure in the accumulator has to be increased and a larger accumulator used.
A second disadvantage is that in order to reach the internal elements of the head almost entire disassembly of the head is required thus resulting in considerable time being taken up for cleaning and maintenance of the head.
A third disadvantage concerns the difficulty of removing sand from the walls of the tank, owing to the fact that the jet of air is guided in a manner as first to impact the sand in the internal space of the tank, and second to flow along a peripheral hollow space provided between the outer wall of the tank and an internal net for entrapping the sand, the net having the purpose of letting a flow of air pass through it for detaching the sand from the tank. Of course, the first impact of the jet of air against the mass of sand to blow it into the mould or core-box would push the sand against the internal net thus hampering the detachment of the sand and its deposition into the mould or core-box.
A fourth disadvantage is that the gate which controls communication from the hopper to the tank can be clogged by the sand, and is subjected to continuous pressure pulses caused by jets of air against the tank, which pulses cause the gate sealing packings to wear out quickly.